1. Field of the Invention
This invention relates to a plastic container for placing a photographic film cartridge.
2. Description of the Prior Art
At the present time, most of the container bodies for photographic film cartridge are made of plastic and molded by injection molding. The form is, for example, shown in U.S. Pat. No. 4,639,386.
The container, as illustrated in FIG. 1, consists of container body 1 and cap 2, and it can protect a photographic film cartridge placed therein in an airtight state merely by fitting the cap 2 to the container body 1. The container body 1 is in cylindrical form and has a bottom. The opening end portion 3 is slightly thickened, and a round groove 4 is formed circumferentially on the inside thereof. The cap 2 is composed of relatively thick flange 5, peripheral wall portion 6 formed downward from the inner end of the flange 5 and protruded center portion 7 for receiving the core of the film cartridge (not illustrated). Round rib 8 for fitting to the groove 4 is formed near the center of the peripheral wall portion 6, and as shown in FIG. 2, it contacts the bottom portion 9 of the groove 4 to form a sealing state.
It is known to form such a container body 1 from propylene-ethylene random copolymer resin (Japanese Patent KOKAI No. 63-193142) which is stronger than homopolypropylene resin in dropping strength. However, when the ethylene unit is incorporated in polypropylene resin, Rockwell hardness decreases. Wear resistance also decreases, and white powder is generated by the friction with the film cartridge or the like. It is known to add an organic nucleating agent in order to prevent white powder generation by increasing the rigidity of the container body. The blending effect of organic nucleating agent varies according to the content of ethylene unit, properties of propylene-ethylene random copolymer resin and the like. While, organic nucleating agent is sublimed at a high temperature, and the vapor is deposited by cooling to produce white powder. Moreover, white powder is also generated by blending or thermal decomposition so as to adhere to the parting portion and the like of the mold. Since white powder adheres to the mold, it is necessary to interrupt molding at a prescribed intervals to remove the white powder. This is a great problem for automatization or unmanned continuous molding. Moreover, since propylene-ethylene random copolymer resin itself has the property to be whitened by dropping shock and is inferior in transparency, it was never put to practical use for container bodies for photographic film cartridges, though it is excellent in impact strength.